Specialist
A descriptive signal: one language carries more than 80 percent of a developer's output, showing deep single-stack focus.
What it tells you about a developer
Match the specialty to the role's core stack and you get someone contributing at depth immediately. Check the specialty language against your requirement before anything else on the profile.
Specialist is descriptive and carries no judgment on its own. Deep focus in one stack usually means the developer handles that stack's hardest problems and knows its failure modes cold. The reading becomes useful next to a role: a Rust systems role wants a Rust specialist, and a scrappy early-stage role may want breadth.